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DOI: 10.1039/A606704B (Paper) Reference Section for: J. Chem. Soc., Perkin Trans. 2, 1997, 971-976

Rates of thermolysis of azidobenzenes in solution: large stabilizations of transition states by charge transfer from electron-donor substituents

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Leonard K. Dyall, Gerrit L’abbé and Wim Dehaen

Abstract

Introduction of +R type para substituents into azidobenzenes causes very large increases in rate of thermolysis, up to 225-fold. The rates of nitrobenzene solutions at 120 °C follow a Hammett-type linear free energy relationship log k = -5.44 - 2.33σI - 1.48 R+ which indicates conjugative stabilization of a nitrene-like transition state. ortho-Substituents of the +R type causes still larger rate enhancements, up to 456-fold for 2-amino, which identify a special resonance proximity effect. It is suggested that the very high rates reported for such α-azidoheterocycles as 2-azidothiophene are due to similar resonance stabilizations and not to ring-opening concerted with nitrogen loss.

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